The present invention relates generally to solid composite propellant compositions and more particularly to solid composite propellant compositions useful as gas generators.
Recently, there has been a great demand for new gas generating propellants which are cool burning, non-corrosive and yield a high volume of gas and low solid particulates because attempts to improve existing gas generating compositions have been unsuccessful for various reasons. For example, while the addition of certain modifiers has lowered the flame temperature and increased gas production, these same modifiers have contributed to the production of undesirable corrosive products. In turn, other modifiers utilized in the past, while not producing corrosive materials, have not succeeded in lowering the flame temperature significantly or of increasing gas evolution.
The usual gas generator composition, known in gas generator technology as the "propellant", is comprised of ammonium nitrate oxidizer with rubbery binders or in pressed charges. Various chemicals such as guanidine nitrate, oxamide and melamine are used in the propellant to aid ignition, give smooth burning, modify burning rates and give lower flame temperatures.
Ammonium nitrate is the most commonly used oxidizer since it is exceptionally effective per unit weight and yields a non-toxic and noncorrosive exhaust at low flame temperatures. Further, it contributes to burning rates lower than those of other oxidizers. Ammonium nitrate is cheap, readily available and safe to handle. The main objection to ammonium nitrate is that it undergoes certain phase changes during temperature variations causing cracks and voids if any associated binder is not sufficiently strong and flexible to hold the composition together.
Ammonium nitrate compositions are hygroscopic and difficult to ignite, particularly if small amounts of moisture have been absorbed. Since said compositions do not sustain combustion at low pressures, various combustion catalysts are added to promote ignition and low pressure combustion as well as to achieve smooth, stable burning. Gas generator compositions used for air bags should contain no metallic additives or even oxidizers such as ammonium perchlorate, because these give erosive and corrosive exhaust gases respectively. Commonly used additives, such as ammonium dichromate, copper chromite, etc., are disadvantageous since they all produce solids in the exhaust gases.
Gas generator compositions are usually manufactured by a pressing or by an extruding and compression molding technique. The solid particles are formed and the composition is broken up into bits ("granulated") with appropriate granulator-type equipment.
After granulation, the composition is loaded into molds of the required shapes and pressed to about 7000 psi (4921 kg/cm.sup.2). With certain types of binder, the molds are heated to about 180.degree. F. (82.degree. C.) until the composition is cured or vulcanized. The grain is then potted into the gas generator cases. The molds, mills and extrusion equipment are costly; the lengthy process time further increases the cost of manufacture. It is especially difficult to produce large grains by this technique.
The art is replete with instances of compositions containing a guanidine-type compound together with an oxidizer, such as ammonium nitrate. For example, in U.S. Pat. No. 3,031,347, guanidine nitrate and ammonium nitrate are listed together at column 2, as well as in Examples 3 and 5. However, compared with the present invention, not only does the guanidine compound lack an amino group, as in the aminoguanidine nitrate embodiment, but the composition disclosed in the patent is not a eutectic solution-forming mixture. Likewise, see U.S. Pat. No. 3,739,574, col. 2, in the Table. On the other hand, U.S. Pat. No. 3,845,970, at column 3, discloses a list of solid compositions for generating gas in a shock absorption system. Among the components of the various compositions are ammonium nitrate and aminoguanidine nitrate. The two materials are not disclosed in admixture and, obviously, are not in a eutectic composition. Similarly, U.S. Pat. No. 3,954,528, discloses new solid composite gas generating compositions. Among the ingredients mentioned are ammonium nitrate and triamino- guanidine nitrate. See Examples 2 through 5. However, neither the specific components of the aminoguanidine nitrate compositions at hand, nor any eutectic compositions, are disclosed therein.
In U.S. Pat. No. 4,111,728, the inventor discloses ammonium nitrate with small amounts of guanidine nitrate. See column 2 and the table at columns 3-4. However, the compositions do not include aminoguanidine nitrate and do not characterize any composition as forming a eutectic solution.
U.S. Pat. No. 5,125,684 also discloses propellant compositions containing dry aminoguanidine nitrate and an oxidizer salt containing a nitrate anion. However, the disclosure is deficient with respect to the present invention since it fails to disclose the specific combination of components of the present invention and does not mention eutectics.
Finally, U.S. Pat. No. 5,336,439 concerns salt compositions and concentrates used in explosive emulsions. As disclosed at columns 37 and 38, ammonium nitrate is one of the ingredients for forming the patentee's composition, while at column 20, line 51, aminoguanidine is indicated as also being an appropriate component. Nevertheless, like the other disclosures mentioned, the patent fails to disclose a specific composition including the same nitrates as are disclosed herein and clearly does not teach a eutectic composition containing said components.